In the metal working arts it often becomes necessary to bend a steel tube or conduit for one purpose or another. Some examples of pipe bending requirements include the fabrication of steel loops which form the dividers of cattle stalls as illustrated in U.S. Pat. to Anderson No. 3,726,257; in the plumbing art; in the formation of electrical conduits by electricians and other situations in which it becomes necessary to bend pipes. There are various known pipe bending apparatuses or appliances. Most popular of such types include a circular die which is pushed against the central portion of a pipe being restrained on opposite sides of the die by stop members. As the die is pushed between the stop members the conduit assumes basically a U-shape. Because the stop members are generally stationary, it is not possible to accomplish an overbend sufficient to allow for the resiliency of the metal, so that after the pipe is formed into its U-shape and removed from the die the legs tend to spring outwardly and are not really parallel. In order to further complete the bend to make the legs absolutely parallel becomes a time consuming and expensive procedure.
Several apparatuses have been developed in which one end of a pipe is held while the remainder of the pipe is bent around a circular die by a rotating force transmitting member. Such apparatuses are disclosed in U.S. Pat. to Middleton No. 2,762,416; Paine No. 3,546,917; Sakamato No. 4,052,875; and Shimizer No. 4,009,601. While it is possible to more easily realize a true parallel relationship between the legs of the resulting U-shaped member with such devices there are various problems which have arisen and which have not to date been solved. One such problem exists when the force transmitting member rotates around the stationary circular die, there is a tendency for the pipe to slip and be pulled along the periphery of the circular die, so that it is impossible to establish a resulting U-shaped member in which the legs are of equal length. In other words, it is difficult to maintain one end of the pipe back against a stop member as the force transmitting member tends to pull the pipe away from such stop member.
Another problem exists when the force transmitting member is rotated with respect to the circular die, if the force transmitting member is positioned too close to the peripheral surface of the die, the walls of the pipe will tend to collapse inwardly before the pipe as a whole begins to bend. Therefore, a wrinkled or collapsed wall configuration will occur in the area of the bend which may become unsightly or, even worse in the case of a conduit through which a fluid passes, may cause inconsistent cross-sections with a resulting adverse effect on the fluid dynamics of the system.
Also with such known apparatuses as are disclosed in the aforementioned prior patents it becomes necessary to change dies whenever a pipe or conduit of a different diameter is desired to be bent. In some industries or craft, it is very important to be able to bend pipe of different diameters, rather than always bending a pipe of the same diameter.